Re: [Qemu-devel] [PATCH V3 0/4] vfio: Introduce Live migration capability to vfio_mdev device

[Alex Williamson <alex.williamson@redhat.com>]

[cc +Juan]

On Mon,  5 Mar 2018 14:00:49 +0800
Yulei Zhang <yulei.zhang@intel.com> wrote:

> Summary
> 
> This series RFC would like to resume the discussion about how to
> introduce the live migration capability to vfio mdev device. 
> 
> By adding a new vfio subtype region VFIO_REGION_SUBTYPE_DEVICE_STATE,
> the mdev device will be set to migratable if the new region exist
> during the initialization.  
> 
> The intention to add the new region is using it for mdev device status
> save and restore during the migration. The access to this region
> will be trapped and forward to the mdev device driver, it also uses 
> the first byte in the new region to control the running state of mdev
> device, so during the migration after stop the mdev driver, qemu could
> retrieve the specific device status from this region and transfer to 
> the target VM side for the mdev device restore.
> 
> In addition,  we add one new ioctl VFIO_IOMMU_GET_DIRTY_BITMAP to help do 
> the mdev device dirty page synchronization during the migration, currently
> it is just for static copy, in the future we would like to add new interface
> for the pre-copy.

Juan had concerns about another dirty bitmap implementation.  I'm not
sure what alternatives we have, but let's loop him in for guidance on
the best migration strategies.  The migration state for a device could
be many gigabytes.

> Below is the vfio_mdev device migration sequence
> Source VM side:
> 			start migration
> 				|
> 				V
>         	 get the cpu state change callback, write to the
>         	 subregion's first byte to stop the mdev device
> 				|
> 				V
> 		 quary the dirty page bitmap from iommu container 
> 		 and add into qemu dirty list for synchronization
> 				|
> 				V
> 		 save the deivce status into Qemufile which is 
>                      read from the vfio device subregion
> 
> Target VM side:
> 		   restore the mdev device after get the
> 		     saved status context from Qemufile
> 				|
> 				V
> 		     get the cpu state change callback
>  		     write to subregion's first byte to 
>                       start the mdev device to put it in 
>                       running status
> 				|
> 				V
> 			finish migration
> 
> V3->V2:
> 1. rebase the patch to Qemu stable 2.10 branch.
> 2. use a common name for the subregion instead of specific for 
>    intel IGD.

But it's still tied to Intel's vendor ID??

Thanks,
Alex


> 
> V1->V2:
> Per Alex's suggestion:
> 1. use device subtype region instead of VFIO PCI fixed region.
> 2. remove unnecessary ioctl, use the first byte of subregion to 
>    control the running state of mdev device.  
> 3. for dirty page synchronization, implement the interface with
>    VFIOContainer instead of vfio pci device.
> 
> Yulei Zhang (4):
>   vfio: introduce a new VFIO subregion for mdev device migration support
>   vfio: Add vm status change callback to stop/restart the mdev device
>   vfio: Add struct vfio_vmstate_info to introduce put/get callback
>     funtion for vfio device status save/restore
>   vifo: introduce new VFIO ioctl VFIO_IOMMU_GET_DIRTY_BITMAP
> 
>  hw/vfio/common.c              |  34 +++++++++
>  hw/vfio/pci.c                 | 171 +++++++++++++++++++++++++++++++++++++++++-
>  hw/vfio/pci.h                 |   1 +
>  include/hw/vfio/vfio-common.h |   1 +
>  linux-headers/linux/vfio.h    |  29 ++++++-
>  5 files changed, 232 insertions(+), 4 deletions(-)
>